L9- Glycolysis Flashcards
LO1: Name the tissues in which glucose entry is insulin-dependent vs. insulin-independent.
INSULIN DEPENDENT
- adipose tissue
- muscle
INSULIN INDEPENDENT
-all other tissues
LO2: Glucokinase vs. hexokinase- describe the differences in their kinetic properties and how this affects their function
GLUCOKINASE
- traps glucose in liver and pancreatic B-cells
- Km for glucose: ~10mM (will respond to higher concentrations, doesn’t plateau early
- high Vmax
- not inhibited by glu-6-phosphate
- induced by insulin (increases its affinity for glucose so it can take up excess glucose and store it after a meal)
HEXOKINASE
- traps glucose in all tissues except liver and pancreatic B-cells
- Km for glucose: ~0.1mM (=high affinity, so its always saturated; only glu-6-phosphate inhibition would bring its activity below Vmax)
- low Vmax (because it gets saturated quickly)
- inhibited by glu-6-phosophate
- induced by high levels of glucose
- not dependent on insulin (so it is almost always binding glucose and taking it in)
LO3: Compare/contrast the role of glycolysis in muscle, liver, red blood cells, and brain
muscle- role is to supply energy for muscle contraction
liver- in the fed state, role is to serve as pathway for excess glucose to be converted to fat for storage
in the fasted state, its reverse reactions are used in gluconeogenesis
red blood cells- role is to provide all of its ATP (RBCs don’t have mitochondria and can’t do oxidative metabolism)
brain- role is to provide its primary fuel (glucose oxidized completely to CO2 and H2O)
LO4: Cellular location of the glycolytic enzymes Hexokinase Glucokinase Aldolase PGI GAPDH PFK-1 PK
Hexokinase- cytosol of all tissues except liver
Glucokinase- cytosol of liver cells and pancreatic B-cells
ALSO CYTOSOLIC:
Aldolase: cleaves six-carbon chain into two, three carbon fragments
PGI: phosphoglucoisomerase; converts Glu-6-phosphate into its isomer, fructose-6-phosphate
GAPDH (G3P-DH): glyceraldehyde 3-phosphate dehydrogenase reversibly catalyzes the oxidation and phosphorylation of G3P to the energy-rich intermdiate 1,3BPG
PFK-1: catalyzes the addition of the phosphate to C-1 of F6P; rate limiting step in glycolysis and the reaction is also irreversible
PK: pyruvate kinase, facilitates transfers of phosphate bonds to ATP (substrate level phosphorylation) along with phosphoglycerate kinase
LO5: Name the enzymes in glycolysis that utilize ATP, generate ATP, and generate NADH
UTILIZE ATP
- hexokinase/glucokinase use 1
- PFK-1 uses 1
GENERATE ATP
- phosphoglycerate kinase makes 2
- pyruvate kinase makes 2
GENERATE NADH
-G3P-DH generatEes 2
LO6: Explain the relationship between G3P-DH and LDH in aerobic vs. anaerobic glycolysis
G3P-DH generates NADH (when P is bound to create 1,3-BPG)
NADH can be reoxidized via ETC to synthesis 2-3 ATPs depending on shuttle (aerobic conditions)
NADH can be used to reduce pyruvate to lactate so that glycolysis can continue
LO7: Identify the primary site of regulation in glycolysis, the enzyme, and its function
PFK-1: catalyzes the committed (irreversible) + rate-limiting step of glycolysis, the conversion of fructose-6-phosphate and ATP to fructose 1,6-bisphosphate and ADP
-uses 1 ATP
LO7: How is the rate-limiting enzyme in glycolysis regulated?
Allosteric regulation-ACTIVATION by increasing the affinity/decreasing the Km of the enzyme (PFK-1) for the substrate (F-6-P)
- AMP in muscle
- Fructose-2,6-bisphosphate in liver
- (activated by low energy state)
Allosteric regulation-INHIBITION by decreasing the affinity/increasing the Km of the enzyme (PFK-1) for the substrate (F-6-P)
-ATP
-citrate
(inhibited by high energy state)
LO7: How does the regulation of the rate-limiting enzyme in glycolysis differ between muscle and liver?
IN LIVER
- inhibited by ATP and citrate
- activated by fructose-2,6-bisphosphate
- F-2,6BP is increased by insulin and decreased by glucagon to promote breakdown of glucose so that pyruvate can get converted to fat)
IN MUSCLE
- inhibited by ATP and citrate
- activated by AMP (indicates muscle is using a lot of energy and more needs to be extracted through glycolysis)
LO8: Name two enzymes that are secondary sites for regulation of glycolysis; how are they regulated?
PYRUVATE KINASE-regulation type depends on isozyme
liver: allosteric activation by F-1,6,-P2, inhibition by ATP and alanine
covalent inhibition by cAMP-dependent protein kinase (phosphorylation)
muscle: allosteric activation by F-1,6,-P2, inhibition by ATP
HEXOKINASE
-negative feedback inhibition–>build-up of Glu-6-P, a product of the reaction, will inhibit hexokinase
LO9: Compare/contrast products of aerobic vs. anaerobic glycolysis
AEROBIC 2 pyruvate 2 NADH 2 ATP -NADH can then be reoxidized vita ETC to produce more ATP
ANAEROBIC
2 lactate
2 ATP
-NADH used to reduce pyruvate to lactate
L10: Name three intermediates generated by glycolysis that are branch points for reactions in other pathways
Glucose-6-phosphate: also used in pentose phosphate pathway (gets dehydrogenated in the committed step to generate NADPH and ribulose-5-phosphate), and can be converted to glycogen for storage
Dihydroxyacetone phosphate (DHAP): used to synthesize fructose 1,6-bisphosphate, and is reduced to glycerol-3-phosphate to synthesize triglycerides in adipose tissue
Glyceraldehyde-3-P: isomer of DHAP, also participates in pentose phosphate pathway
LO11: Name an enzyme in glycolysis that will result in hemolytic anemia if it is deficient
Pyruvate kinase: if deficient, will result in impaired ATP synthesis and accumulation of 2,3-BPG, which decreases the O2 affinity for Hb and overall results in reduced energy for RBC
LO12: Name two types of cells that utilize anaerobic glycolysis as a major or sole source of energy
RBCs, because they lack mitochondria
Bacteria
Skeletal muscle under low-oxygen conditions (exercise, stress)
